I’m an individual. Can I use private relay when sending emails?
How do I use private relay to send and receive emails
About iCloud Private Relay --> https://support.apple.com/HT212614
Learn how iCloud Private Relay—part of an iCloud+ subscription—helps protect your privacy when you browse the web in Safari.
From what I can tell, Private Relay has nothing to do with email.
If you mean Hide My Email, you might want to read up on the details of that service. It is not an anonymous email account for general email use.
Learn more about Hide My Email and iCloud+ --> https://support.apple.com/HT212519
What is Hide My Email? --> https://support.apple.com/HT210425